1. Field of the Invention
The present invention relates generally to overhead ‘garage’ doors, of the type used to close large openings in residential and commercial buildings. More particularly, the present invention relates to overhead doors of the sectional type, and to a drive arrangement for such doors.
2. Description of Related Art
Sectional garage doors are well known in the art. Although the design of sectional garage doors can significantly differ, certain components are common to such door systems. Thus a typical sectional garage door has a door curtain made of a plurality—usually four or more—panel sections hinged together at their longitudinal edges about horizontal hinge axes.
A pair of generally inverted L-shaped guide tracks is mounted to the building, one at each side of the door opening, with the vertical leg of the L being at the side of the door opening and the horizontal leg being above the level of the opening and extending back into the building space. The junction of the horizontal and vertical legs of the track is radiussed.
The door includes a plurality of rollers mounted on the opposite sides of the door sections, which follow the guide tracks to guide movement of the door curtain between a closed (lowered) position in which the door is vertical and closes off the door opening and an open (raised) position where the door is stored overhead in a horizontal orientation.
Since a sectional door is relatively large and heavy, it is commonplace to provide a counter-balancing spring system which loads up one or more torsion or extension springs as the door is lowered, so that the spring tension assists raising of the door. Such systems are commonly used even where the door is power operated.
A typical counter-balancing system includes one or more torsion springs on a horizontal torsion shaft which is secured to the building structure above the door opening. The shaft has a cable drum with a cable connected to the bottom section of the door. As the door is lowered, the withdrawal of the cable causes the shaft to turn, winding up the torsion spring. The number and size of the springs is selected so that spring tension is selected to counterbalance part of the weight of the door, so that the door is easier to raise.
One type of power operator drive mechanism comprises a motor drive and belt drive arrangement mounted on a horizontal track suspended from the building structure above and behind the centre of the door opening, parallel to but above the plane of the horizontal legs of the L-shaped tracks, with a linkage connecting to the centre top of the sectional door. This arrangement requires additional fixing and increases the headroom required for the installation, ultimately reducing the height of the door that can be installed in situations where headroom is limited.
WO 2007/051237 and WO 2011/003152 disclose garage door arrangements which the torsion spring, and optionally the motor, is mounted on the door curtain, providing advantages in manufacture and installation.
There remains a need for an improved drive mechanism for sectional garage doors.